Welcome to the Transionospheric Radio Link - Near-real-time TEC maps service

The service "Transionospheric Radio Link - Near-real-time TEC maps" aims to provide maps of the Total Electron Content (TEC) no more than 5 minutes after observation (near-real-time). Supplementary materials are measurements from ionosondes (URSI parameters), height of maximum electron density in the F2 layer (hmF2). The Smoothed Sunspot Number (SSN) and the solar flux density from the entire solar disk at 10.7 cm (F10.7) are solar parameters contributing to this service. They are proportional to the level of ionisation in the ionosphere and therefore commonly used for TEC models.

This service addresses the needs of trans-ionospheric radio links users. This includes primarily Global Navigation Satellite System (GNSS) users and service providers, using GNSS single frequency services (e.g. EGNOS users and typical GNSS mass market users), GNSS multi-frequency services (e.g. aeronautical systems, geodetic users, Real-Time Kinematik) and users of satellite data communications (e.g. Search and Rescue, Air Traffic, etc.) and other space-based services affected by the ionosphere (e.g. radars, altimetry, radioastronomy, etc.).

The URSI parameters include hmF2 and ITEC derived from true-height analysis of ionosonde data. This data is valuable for the comparison and validation against GPS TEC measurements.

This service is implemented through a combination of products, tools and alerts which can be found through the following sections along with expert support provided by the teams constituting the SWE Network. Should you require further guidance in the use of this service, or have specific questions about any aspects of the service presented here, don’t hesitate to contact the Helpdesk.

The service is implemented through the following set of assets:

• Ionosphere Monitoring and Prediction Center (IMPC) provided by the German Aerospace Center (DLR);
• Real-Time Ionosphere Monitor (RTIM) provided by the Norwegian Mapping Authority (NMA);
• European Ionosonde Service (EIS) provided by National Observatory of Athens (NOA);
• Ionospheric Scintillation Monitoring (ISM) developed by Collecte Localisation Satellites (CLS) and IEEA (currently under maintenance);
• ESA/ESOC Ionosphere Monitoring Facility, IONMON;
• Nowcasting of TEC over Italy provided by Istituto Nazionale di Geofisica e Vulcanologia (INGV);
• SRC RIOBorówiec Riometer provided by Space Research Centre Polish Academy of Sciences (SRC);
• Regional volumetric reconstructions of ionospheric electron density product TomoScand provided by the Finnish Meteorological Institute (FMI) and University of Oulu;
• UPC-IonSAT service provided by the Universitat Politècnica de Catalunya (UPC).

This service page is curated by the ESC Ionospheric Weather.  For further information, please contact SSCC Helpdesk. 

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Introduction

The Total Electron Content (TEC) is defined as the integral of the electron density along the ray path between satellite and receiver. Thus, TEC provides the number of electrons per square metre. The most frequently used unit is 1TECU = 1x10¹⁶ electrons / m².

TEC measurements are available since the middle of the 1950s. Various techniques have been applied. The basic three methods using radio techniques for deriving TEC are:

• Faraday rotation,
• Group delay and
• differential carrier phase.

Commonly, radio signal transmission from various satellites is used to derive TEC. TEC data can be derived from satellite radio beacon operations, but the data base is limited due to its geographic coverage. Today, GNSS measurements provide an excellent data coverage for the generation of TEC maps. But also measurements from ionospheric sounders (e.g. ionosondes), making routine measurements of the bottom side ionosphere, can be used to derive TEC and generate maps. In this case, models are required to consider the top side ionosphere (cf. EIS - Near-real-time TEC, below).

Application

TEC measurements can be used by system designers or operators to make a correction for the time delay effects of the ionosphere on their system. Continuous measurements of carefully calibrated TEC are today required for many applications, e.g.

• users of satellites for precise time transfer
• advanced ranging systems
• radio astronomers, who require a knowledge of the effects of the ionosphere on their measurement accuracy

Furthermore, TEC measurements essentially contribute to the investigation of the physics in the upper atmosphere and ionosphere.

Key Products

Near-real-time TEC maps

TEC maps present the vertical integral of the electron density. Near-real-time TEC maps are very soon after completion of the measurements. This services provides different types of TEC maps:

• IMPC - Near-real-time TEC maps are provided with global coverage and for the European region. They are provided with 5 minutes latency and 15 minutes temporal resolution. Both products differ in the applied background model. A dedicated European TEC background model allows a higher quality TEC product for the European region. Each TEC map is provided along with a TEC error map.
• RTIM - Near-real-time TEC maps are high resolution TEC maps for the high-latitude region around the Scandinavian countries (50°N – 80°N, 10°W – 40°E). Since the data coverage is high, no TEC background model is necessary. The temporal resolution is 5 minutes and the spatial resolution is 1° x 1° in latitude and longitude. The quality of the RTIM - TEC maps is presented by the Grid Ionospheric Vertical Error (GIVE) values. The GIVE is an upper bound on 99% of the TEC error.
• ISM - Near-real-time TEC maps have a global coverage. Their temporal resolution is 1 hour.
• IONMON - The Ionosphere Monitoring Facility IONMON delivers animated maps of the global distribution of the Total Electron Content (TEC) & the TEC Root Mean Square errors (RMS). The animations cover 24 hours with an 1-hour time resolution. Both TEC and RMS levels are displayed in TEC units (1 TECU = 10^16 el/m^2) on the colour maps. The range of values, displayed on the colour bars underneath the maps, is fixed from 0 to 60 TECU for TEC and from 0 to 10 TECU for RMS. In case TEC and RMS values exceed the aforementioned fixed limits, the maximum value will be shown next to the colour bar. The maps are provided by the ESA/ESOC Navigation Support Office (OPS-GN).

3D electron density

To obtain three-dimensional information on electron density the service provides TomoScand, a volumetric reconstruction of electron density in the altitude range 100-800 km based on dual frequency signals from both low Earth orbit satellites (150 and 400 MHz) and the Global Positioning System (GPS).

URSI parameters

URSI parameters are derived from ionosonde observations. They help interpreting the ionospheric conditions. This service provides URSI parameters, which are currently provided by the EIS service.

Ionospheric Disturbances

For most users, the degree of perturbation of the ionosphere is of high interest. Currently, this service provides Rate Of change of TEC Index (ROTI) observations. ROTI is related to scintillations. Key products are

• ROTI maps are provided by IMPC for Europe and by RTIM for FennoScandinavia.
• Additionally, the SUA activity provides ROT along the flight paths' of the three Swarm satellites.

Auxiliary Information

This section provides links to web pages or resources that are not part of the ESA Space Weather Network or esa.int domain. These sites are not under ESA control and therefore ESA is not responsible for any of the information or links that you may find there.

Other European Ionosphere Services

• Space Weather Application Service - Ionosphere (SWACI), one of the first prototypes for a near-real-time ionosphere data service in Europe, has been established in 2005 by the German Aerospace Center. It is currently transferred into the operational service Ionosphere Monitoring and Prediction Center (IMPC)
• To better classify the ionosphere and forecast its disturbances over Europe, a data collection endeavour called the European Digital Upper Atmosphere Server (DIAS) was initiated in 2004 by a consortium formed around several European ionospheric stations that transmit in real-time ionospheric parameters automatically scaled. The DIAS project is a collaborative venture of eight institutions funded by the European Commission eContent Programme.

Reference documents

• ECSS-E-ST-10-04C Rev.1 Space environment (15 June 2020)

Contact

For further information, please contact SSCC Helpdesk. 

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